The goal is to improve the effectiveness of the current therapy of inborn errors of urea synthesis. Of the two principal pharmaceutical agents currently in use one (sodium phenylacetate) has an offensive odor and the other (sodium benzoate) has half the effectiveness of the first. These studies are designed to test the acceptability of a second generation prodrug for phenylacetate, sodium phenylbutyrate which does not have the repugnant odor of phenylacetate. Because of its greater acceptability and greater effectiveness a study will be done of high dose phenylbutyrate which may obviate the need for sodium benzoate. Theoretical considerations suggest that sodium phenylbutyrate in high dosage will activate the biosynthesis of an amount of phenylacetylglutamine nitrogen that will completely substitute for urea nitrogen as a vehicle for waste nitrogen synthesis. The specific methods will include a study of the pharmacology of sodium phenylbutyrate and a study of long term outcome. In addition a study will be done to test a possible role of dietary citrate supplementation in the treatment of argininosuccinase deficiency.